Metal-free, bio-based polyester developed

RESEARCHERS in the US have developed a fully recyclable biopolyester from a non-metal catalyst, which they believe could be the first step towards a truly sustainable biopolymer.

In recent years, the most promising candidate for making a recyclable biopolymer has been gamma-butyrolactone (GBL), which can be made from bio-derived succinic acid. While GBL can be turned into a useful polymer, poly-GBL or PGBL, the process is difficult, the reaction conditions needed are extremely harsh, and require a metal catalyst. Traces of the catalyst can remain in the polymer, making it unsuitable for some purposes, such as biomedical applications. Now Eugene Chen, a professor at Colorado State University, and postdoctoral student Miao Hong, believe they have found a solution.

Chen and Hong use a very strong organic base, tert-Bu-P₄, as the catalyst to initiate the reaction, a ring-opening polymerisation. The reaction to produce the PGBL works at temperatures down to -40?C and at ambient pressure. Around 90% of the monomer is converted in around four hours. The polymer is produced as a powder, which can be easily cast into different shapes in the same way as petroleum-based polyesters.

Applying heat to the PGBL polyester breaks it down completely for easy recycling and waste minimisation.

“The PGBL obtained by the current organopolymerisation is completely recyclable back to its monomer in the pure state upon heating the bulk polymer,” the researchers write.

The researchers say the metal-free biopolyester could find most uses for medical applications and in the microelectronics industry, where any metal content is undesirable.

Angewandte Chemie DOI: 10.1002/anie.201601092View